Virological characteristics of the SARS-CoV-2 Omicron BA.2 spike.

Soon after the emergence and global spread of the SARS-CoV-2 Omicron lineage BA.1, another Omicron lineage, BA.2, began outcompeting BA.1. The results of statistical analysis showed that the effective reproduction number of BA.2 is 1.4-fold higher than that of BA.1. Neutralization experiments revealed that immunity induced by COVID vaccines widely administered to human populations is not effective against BA.2, similar to BA.1, and that the antigenicity of BA.2 is notably different from that of BA.1. Cell culture experiments showed that the BA.2 spike confers higher replication efficacy in human nasal epithelial cells and is more efficient in mediating syncytia formation than the BA.1 spike. Furthermore, infection experiments using hamsters indicated that the BA.2 spike-bearing virus is more pathogenic than the BA.1 spike-bearing virus. Altogether, the results of our multiscale investigations suggest that the risk of BA.2 to global health is potentially higher than that of BA.1.

Virological characteristics of the SARS-CoV-2 Omicron BA.2 subvariants, including BA.4 and BA.5.

After the global spread of the SARS-CoV-2 Omicron BA.2, some BA.2 subvariants, including BA.2.9.1, BA.2.11, BA.2.12.1, BA.4, and BA.5, emerged in multiple countries. Our statistical analysis showed that the effective reproduction numbers of these BA.2 subvariants are greater than that of the original BA.2. Neutralization experiments revealed that the immunity induced by BA.1/2 infections is less effective against BA.4/5. Cell culture experiments showed that BA.2.12.1 and BA.4/5 replicate more efficiently in human alveolar epithelial cells than BA.2, and particularly, BA.4/5 is more fusogenic than BA.2. We further provided the structure of the BA.4/5 spike receptor-binding domain that binds to human ACE2 and considered how the substitutions in the BA.4/5 spike play roles in ACE2 binding and immune evasion. Moreover, experiments using hamsters suggested that BA.4/5 is more pathogenic than BA.2. Our multiscale investigations suggest that the risk of BA.2 subvariants, particularly BA.4/5, to global health is greater than that of original BA.2.

Attenuated fusogenicity and pathogenicity of SARS-CoV-2 Omicron variant.

The emergence of the Omicron variant of SARS-CoV-2 is an urgent global health concern1. In this study, our statistical modelling suggests that Omicron has spread more rapidly than the Delta variant in several countries including South Africa. Cell culture experiments showed Omicron to be less fusogenic than Delta and than an ancestral strain of SARS-CoV-2. Although the spike (S) protein of Delta is efficiently cleaved into two subunits, which facilitates cell-cell fusion2,3, the Omicron S protein was less efficiently cleaved compared to the S proteins of Delta and ancestral SARS-CoV-2. Furthermore, in a hamster model, Omicron showed decreased lung infectivity and was less pathogenic compared to Delta and ancestral SARS-CoV-2. Our multiscale investigations reveal the virological characteristics of Omicron, including rapid growth in the human population, lower fusogenicity and attenuated pathogenicity.

Chimeric provirus of bovine leukemia virus/SMAD family member 3 in cattle with enzootic bovine leukosis.

Bovine leukemia virus (BLV) is a member of the family Retroviridae that causes enzootic bovine leukemia (EBL). However, the association between BLV infection and EBL development remains unclear. In this study, we identified a BLV/SMAD3 chimeric provirus within CC2D2A intron 30 in monoclonal expanded malignant cells from a cow with EBL. The chimeric provirus harbored a spliced SMAD3 sequence composed of exons 3-9, encoding the short isoform protein, and the BLV-SMAD3 chimeric transcript was detectable in cattle with EBL. This is the first report of a BLV chimeric provirus that might be involved in EBL tumorigenesis.

Virological characteristics of the SARS-CoV-2 Omicron EG.5.1 variant.

In middle to late 2023, a sublineage of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron XBB, EG.5.1 (a progeny of XBB.1.9.2), is spreading rapidly around the world. We performed multiscale investigations, including phylogenetic analysis, epidemic dynamics modeling, infection experiments using pseudoviruses, clinical isolates, and recombinant viruses in cell cultures and experimental animals, and the use of human sera and antiviral compounds, to reveal the virological features of the newly emerging EG.5.1 variant. Our phylogenetic analysis and epidemic dynamics modeling suggested that two hallmark substitutions of EG.5.1, S:F456L and ORF9b:I5T are critical to its increased viral fitness. Experimental investigations on the growth kinetics, sensitivity to clinically available antivirals, fusogenicity, and pathogenicity of EG.5.1 suggested that the virological features of EG.5.1 are comparable to those of XBB.1.5. However, cryo-electron microscopy revealed structural differences between the spike proteins of EG.5.1 and XBB.1.5. We further assessed the impact of ORF9b:I5T on viral features, but it was almost negligible in our experimental setup. Our multiscale investigations provide knowledge for understanding the evolutionary traits of newly emerging pathogenic viruses, including EG.5.1, in the human population.

Impact of Imprinted Immunity Induced by mRNA Vaccination in an Experimental Animal Model.

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variants has led to concerns that ancestral SARS-CoV-2-based vaccines may not be effective against newly emerging Omicron subvariants. The concept of "imprinted immunity" suggests that individuals vaccinated with ancestral virus-based vaccines may not develop effective immunity against newly emerging Omicron subvariants, such as BQ.1.1 and XBB.1. In this study, we investigated this possibility using hamsters. Although natural infection induced effective antiviral immunity, breakthrough infections in hamsters with BQ.1.1 and XBB.1 Omicron subvariants after receiving the 3-dose mRNA-lipid nanoparticle vaccine resulted in only faintly induced humoral immunity, supporting the possibility of imprinted immunity.

Haplotype networks of SARS-CoV-2 infections in the Diamond Princess cruise ship outbreak.

The Diamond Princess cruise ship was put under quarantine offshore Yokohama, Japan, after a passenger who disembarked in Hong Kong was confirmed as a coronavirus disease 2019 case. We performed whole-genome sequencing of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) directly from PCR+ clinical specimens and conducted a phylogenetic analysis of the outbreak. All tested isolates exhibited a transversion at G11083T, suggesting that SARS-CoV-2 dissemination on the Diamond Princess originated from a single introduction event before the quarantine started. Although further spreading might have been prevented by quarantine, some progeny clusters could be linked to transmission through mass-gathering events in the recreational areas and direct transmission among passengers who shared cabins during the quarantine. This study demonstrates the usefulness of haplotype network/phylogeny analysis in identifying potential infection routes.

Enhanced isolation of SARS-CoV-2 by TMPRSS2-expressing cells.

A novel betacoronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which caused a large respiratory outbreak in Wuhan, China in December 2019, is currently spreading across many countries globally. Here, we show that a TMPRSS2-expressing VeroE6 cell line is highly susceptible to SARS-CoV-2 infection, making it useful for isolating and propagating SARS-CoV-2. Our results reveal that, in common with SARS- and Middle East respiratory syndrome-CoV, SARS-CoV-2 infection is enhanced by TMPRSS2.

Susceptibility of herons (family: Ardeidae) to clade 2.3.2.1 H5N1 subtype high pathogenicity avian influenza virus.

The pathogenicity of the H5 subtype high pathogenicity avian influenza viruses (HPAIVs) in Ardeidae bird species has not been investigated yet, despite the increasing infections reported. Therefore, the present study aimed to examine the susceptibility of the Ardeidae species, which had already been reported to be susceptible to HPAIVs, to a clade 2.3.2.1 H5N1 HPAIV. Juvenile herons (four grey herons, one intermediate egret, two little egrets, and three black-crowned night herons) were intranasally inoculated with 106 50% egg infectious dose of the virus and observed for 10 days. Two of the four grey herons showed lethargy and conjunctivitis; among them, one died at 6 days post-inoculation (dpi). The viruses were transmitted to the other two cohoused naïve grey herons. Some little egrets and black-crowned night herons showing neurological disorders died at 4-5 dpi; these birds mainly shed the virus via the oral route. The viruses predominantly replicated in the brains of birds that died of infection. Seroconversion was observed in most surviving birds, except some black-crowned night herons. These results demonstrate that most Ardeidae species are susceptible to H5 HPAIVs, sometimes with lethal effects. Herons are mostly colonial and often share habitats with Anseriformes, natural hosts of influenza A viruses; therefore, the risks of cluster infection and contribution to viral dissemination should be continuously evaluated. RESEARCH HIGHLIGHTSClade 2.3.2.1 H5N1 HPAIV causes lethal infections in Ardeidae sp.Viruses are transmitted among grey herons.Some herons with HPAIV showed conjunctivitis or neurological symptoms.HPAIV systemically replicated in herons tissues.

The Inhaled Steroid Ciclesonide Blocks SARS-CoV-2 RNA Replication by Targeting the Viral Replication-Transcription Complex in Cultured Cells.

Here, we screened steroid compounds to obtain a drug expected to block host inflammatory responses and Middle East respiratory syndrome coronavirus (MERS-CoV) replication. Ciclesonide, an inhaled corticosteroid, suppressed the replication of MERS-CoV and other coronaviruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of coronavirus disease 2019 (COVID-19), in cultured cells. The 90% effective concentration (EC90) of ciclesonide for SARS-CoV-2 in differentiated human bronchial tracheal epithelial cells was 0.55 µM. Eight consecutive passages of 43 SARS-CoV-2 isolates in the presence of ciclesonide generated 15 resistant mutants harboring single amino acid substitutions in nonstructural protein 3 (nsp3) or nsp4. Of note, ciclesonide suppressed the replication of all these mutants by 90% or more, suggesting that these mutants cannot completely overcome ciclesonide blockade. Under a microscope, the viral RNA replication-transcription complex in cells, which is thought to be detectable using antibodies specific for nsp3 and double-stranded RNA, was observed to fall in the presence of ciclesonide in a concentration-dependent manner. These observations indicate that the suppressive effect of ciclesonide on viral replication is specific to coronaviruses, highlighting it as a candidate drug for the treatment of COVID-19 patients.IMPORTANCE The outbreak of SARS-CoV-2, the cause of COVID-19, is ongoing. New and effective antiviral agents that combat the disease are needed urgently. Here, we found that an inhaled corticosteroid, ciclesonide, suppresses the replication of coronaviruses, including betacoronaviruses (murine hepatitis virus type 2 [MHV-2], MERS-CoV, SARS-CoV, and SARS-CoV-2) and an alphacoronavirus (human coronavirus 229E [HCoV-229E]), in cultured cells. Ciclesonide is safe; indeed, it can be administered to infants at high concentrations. Thus, ciclesonide is expected to be a broad-spectrum antiviral drug that is effective against many members of the coronavirus family. It could be prescribed for the treatment of MERS and COVID-19.

The R2TP complex regulates paramyxovirus RNA synthesis.

The regulation of paramyxovirus RNA synthesis by host proteins is poorly understood. Here, we identified a novel regulation mechanism of paramyxovirus RNA synthesis by the Hsp90 co-chaperone R2TP complex. We showed that the R2TP complex interacted with the paramyxovirus polymerase L protein and that silencing of the R2TP complex led to uncontrolled upregulation of mumps virus (MuV) gene transcription but not genome replication. Regulation by the R2TP complex was critical for MuV replication and evasion of host innate immune responses. The R2TP complex also regulated measles virus (MeV) RNA synthesis, but its function was inhibitory and not beneficial to MeV, as MeV evaded host innate immune responses in the absence of the R2TP complex. The identification of the R2TP complex as a critical host factor sheds new light on the regulation of paramyxovirus RNA synthesis.

Environmental Sampling for Severe Acute Respiratory Syndrome Coronavirus 2 During a COVID-19 Outbreak on the Diamond Princess Cruise Ship.

During a COVID-19 outbreak on the Diamond Princess cruise ship we sampled environmental surfaces after passengers and crew vacated cabins. SARS-CoV-2 RNA was detected in 58 of 601 samples (10%) from case cabins 1-17 days after cabins were vacated but not from noncase cabins. There was no difference in detection proportion between cabins of symptomatic (15%, 28/189; cycle quantification [Cq], 29.79-38.86) and asymptomatic cases (21%, 28/131; Cq, 26.21-38.99). No SARS-CoV-2 virus was isolated from any of the samples. Transmission risk of SARS-CoV-2 from symptomatic and asymptomatic patients may be similar and surfaces could be involved in transmission.

Severe Acute Respiratory Syndrome Coronavirus 2 Infection among Returnees to Japan from Wuhan, China, 2020.

In early 2020, Japan repatriated 566 nationals from China. Universal laboratory testing and 14-day monitoring of returnees detected 12 cases of severe acute respiratory syndrome coronavirus 2 infection; initial screening results were negative for 5. Common outcomes were remaining asymptomatic (n = 4) and pneumonia (n = 6). Overall, screening performed poorly.

A novel 111-nucleotide duplication in the G gene of human metapneumovirus.

In 2017, novel human metapneumovirus (HMPV) A2b subgroup strains with a 111-nucleotide duplication in the G gene was detected by the present team. These strains were related to previously identified HMPV A2b strains with a 180-nucleotide duplication; however, they appeared to be different strains, produced by an independent duplication event. The recent evolution of HMPV suggests that careful monitoring of this virus is required.

Seroepidemiological Prevalence of Multiple Species of Filoviruses in Fruit Bats (Eidolon helvum) Migrating in Africa.

Fruit bats are suspected to be a natural reservoir of filoviruses, including Ebola and Marburg viruses. Using an enzyme-linked immunosorbent assay based on the viral glycoprotein antigens, we detected filovirus-specific immunoglobulin G antibodies in 71 of 748 serum samples collected from migratory fruit bats (Eidolon helvum) in Zambia during 2006-2013. Although antibodies to African filoviruses (eg, Zaire ebolavirus) were most prevalent, some serum samples showed distinct specificity for Reston ebolavirus, which that has thus far been found only in Asia. Interestingly, the transition of filovirus species causing outbreaks in Central and West Africa during 2005-2014 seemed to be synchronized with the change of the serologically dominant virus species in these bats. These data suggest the introduction of multiple species of filoviruses in the migratory bat population and point to the need for continued surveillance of filovirus infection of wild animals in sub-Saharan Africa, including hitherto nonendemic countries.

Genetic and antigenic characterization of H5 and H7 influenza viruses isolated from migratory water birds in Hokkaido, Japan and Mongolia from 2010 to 2014.

Migratory water birds are the natural reservoir of influenza A viruses. H5 and H7 influenza viruses are isolated over the world and also circulate among poultry in Asia. In 2010, two H5N1 highly pathogenic avian influenza viruses (HPAIVs) were isolated from fecal samples of water birds on the flyway of migration from Siberia, Russia to the south in Hokkaido, Japan. H7N9 viruses are sporadically isolated from humans and circulate in poultry in China. To monitor whether these viruses have spread in the wild bird population, we conducted virological surveillance of avian influenza in migratory water birds in autumn from 2010 to 2014. A total of 8103 fecal samples from migratory water birds were collected in Japan and Mongolia, and 350 influenza viruses including 13 H5 and 19 H7 influenza viruses were isolated. A phylogenetic analysis revealed that all isolates are genetically closely related to viruses circulating among wild water birds. The results of the antigenic analysis indicated that the antigenicity of viruses in wild water birds is highly stable despite their nucleotide sequence diversity but is distinct from that of HPAIVs recently isolated in Asia. The present results suggest that HPAIVs and Chinese H7N9 viruses were not predominantly circulating in migratory water birds; however, continued monitoring of H5 and H7 influenza viruses both in domestic and wild birds is recommended for the control of avian influenza.

The zoonotic potential of avian influenza viruses isolated from wild waterfowl in Zambia.

Whilst remarkable progress in elucidating the mechanisms governing interspecies transmission and pathogenicity of highly pathogenic avian influenza viruses (AIVs) has been made, similar studies focusing on low-pathogenic AIVs isolated from the wild waterfowl reservoir are limited. We previously reported that two AIV strains (subtypes H6N2 and H3N8) isolated from wild waterfowl in Zambia harbored some amino acid residues preferentially associated with human influenza virus proteins (so-called human signatures) and replicated better in the lungs of infected mice and caused more morbidity than a strain lacking such residues. To further substantiate these observations, we infected chickens and mice intranasally with AIV strains of various subtypes (H3N6, H3N8, H4N6, H6N2, H9N1 and H11N9) isolated from wild waterfowl in Zambia. Although some strains induced seroconversion, all of the tested strains replicated poorly and were nonpathogenic for chickens. In contrast, most of the strains having human signatures replicated well in the lungs of mice, and one of these strains caused severe illness in mice and induced lung injury that was characterized by a severe accumulation of polymorphonuclear leukocytes. These results suggest that some strains tested in this study may have the potential to infect mammalian hosts directly without adaptation, which might possibly be associated with the possession of human signature residues. Close monitoring and evaluation of host-associated signatures may help to elucidate the prevalence and emergence of AIVs with potential for causing zoonotic infections.

Phylogenetic Analysis of Newcastle Disease Virus Isolated from Poultry in Live Bird Markets and Wild Waterfowl in Zambia.

Poultry production is essential to the economy and livelihood of many rural Zambian households. However, the industry is threatened by infectious diseases, particularly Newcastle disease virus (NDV) infection. Therefore, this study employed next-generation sequencing to characterise six NDV isolates from poultry in Zambia's live bird markets (LBMs) and wild waterfowl. Four NDV isolates were detected from 410 faecal samples collected from chickens in LBMs in Lusaka and two from 2851 wild birds from Lochinvar National Park. Phylogenetic analysis revealed that the four NDVs from LBM clustered in genotype VII and sub-genotype VII.2 were closely related to viruses previously isolated in Zambia and other Southern African countries, suggesting possible local and regional transboundary circulation of the virus. In contrast, the two isolates from wild birds belonged to class I viruses, genotype 1, and were closely related to isolates from Europe and Asia, suggesting the possible introduction of these viruses from Eurasia, likely through wild bird migration. The fusion gene cleavage site motif for all LBM-associated isolates was 112RRQKR|F117, indicating that the viruses are virulent, while the isolates from wild waterfowl had the typical 112ERQER|L117 avirulent motif. This study demonstrates the circulation of virulent NDV strains in LBMs and has, for the first time, characterised NDV from wild birds in Zambia. The study further provides the first whole genomes of NDV sub-genotype VII.2 and genotype 1 from Zambia and stresses the importance of surveillance and molecular analysis for monitoring the circulation of NDV genotypes and viral evolution.

Molecular Epidemiology of Human Metapneumovirus in East Japan before and after COVID-19, 2017-2022.

Human metapneumovirus (hMPV) is genetically classified into two major subgroups, A and B, based on attachment glycoprotein (G protein) gene sequences. The A2 subgroup is further separated into three subdivisions, A2a, A2b (A2b1), and A2c (A2b2). Subgroup A2c viruses carrying 180- or 111-nucleotide duplications in the G gene (A2c 180nt-dup or A2c 111nt-dup ) have been reported in Japan and Spain. The coronavirus disease 2019 (COVID-19) pandemic disrupted the epidemiological kinetics of other respiratory viruses, including hMPV. In this study, we analyzed the sequences of hMPV isolates in Tokyo and Fukushima obtained from 2017 to 2022, i.e., before and after the COVID-19 pandemic. Subgroup A hMPV strains were detected from 2017 to 2019, and most cases were A2c 111nt-dup, suggesting ongoing transmission of this clade, consistent with global transmission dynamics. Subgroup B viruses, but not subgroup A viruses, were detected in 2022 after the COVID-19 peak. Phylogenetic analysis showed that the subgroup B viruses were closely related to strains detected in Yokohama from 2013 to 2016, and strains detected in Fukushima in 2019, suggesting the reappearance of local endemic viruses in East Japan.